Apparatus for establishing communication between a first radio transmitter and receiver and a second radio transmitter and receiver

ABSTRACT

In a radio communication system having a command or base station and one or more controlled or mobile stations, the base station continuously transmits outbound function messages in binary bit form to the mobile stations. Each outbound function message comprises a sequence of binary bits forming a first synchronizing word, a first address word transmitted three times, a second inverted synchronizing word, a second address word transmitted three times, a third inverted synchronizing word, and a command word transmitted three times. All mobile stations receive the outbound messages and synchronize on them, but only that mobile station whose address is transmitted responds. Each mobile station is synchronized when it properly receives two consecutive synchronizing words in sequence, and remains in synchronization unless five consecutive synchronizing word errors occur. The response from the mobile station to the base station is an inbound message also in binary bit form. Each inbound message comprises a preamble followed by the first synchronizing word, the first address word transmitted three times, the second inverted synchronizing word, the second address word transmitted three times, the third inverted synchronizing word, and a response word transmitted three times. This inbound message or response has a bit rate that is 11/2 times the outbound message bit rate so that other mobiles can respond to their respective messages as they are transmitted by the base station. The base station anticipates each inbound message and uses the preamble and the first synchronizing word to synchronize itself with the inbound message. Thus, high speed binary function controls are reliably provided between a base station and one or more mobile stations in the environment of radio frequencies, particularly those in the land mobile service.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is related to the following copending applications:

Ser. No. 576,279, entitled "Apparatus for Indicating Synchronization andOut-of-Synchronization Conditions", filed May 12, 1975;

Ser. No. 576,383, entitled "Message Generator for a Controlled RadioTransmitter and Receiver", filed May 12, 1975;

Ser. No. 576,548, entitled "Apparatus for Indicating Synchronization ofa Radio Receiver With a Radio Transmitter", filed May 12, 1975, nowabandoned;

Ser. No. 576,873, entitled "Diphase to Binary Converter", filed May 12,1975, now abandoned.

BACKGROUND OF THE INVENTION

Our invention relates to function control apparatus, and particularly tofunction control apparatus that is adapted to be used in a radiocommunication system and that uses binary bits or pulses to indicate thedesired functions and responses.

Radio communication systems, particularly those having a command or basestation and one or more mobile stations, are expected to provide manyfunctions over and above the simple call and answer voice communication,and are expected to establish voice communication quickly and reliablyon one of several frequencies or channels. An example of the providedfunction is where a base station needs to determine the status orcondition of a particular mobile station in the system. An example ofestablishing voice communication is where one of several radiofrequencies or channels is to be used for voice communication in a givensystem, such as public safety or in industry.

Accordingly, a primary object of our invention is to provide novelfunction control apparatus that is particularly adapted to be used in aradio communication system.

Another object of our invention is to provide new function controlapparatus for use in two-way radios operating in the land mobileservice.

Another primary object of our invention is to provide apparatus, for usewith radio communication systems, that can obtain information from astation in such a system or that can cause a station in such a system toswitch to selected transmitting and receiving frequencies.

In function control apparatus as described thus far, speed andreliability are important, particularly when the apparatus is used withradio systems at frequencies which are crowded and subject to noise orfading. While there is such function control apparatus available, itsspeed and reliability are not as high as some users require or prefer.

Accordingly, another object of our invention is to provide novelfunction control apparatus for a radio communication system thatprovides relatively high speed operation in a reliable manner, even overthe intended radio frequencies.

SUMMARY OF THE INVENTION

Briefly, these and other objects are achieved in accordance with ourinvention by function control apparatus provided at each station in aradio communication system. A base station usually serves as a commandstation, and transmits outbound messages in binary bit form. Eachoutbound message comprises a first synchronizing word, a first addressword transmitted three times, a second inverted synchronizing word, asecond address word transmitted three times, a third invertedsynchronizing word, and a command word transmitted three times. Theseoutbound messages are transmitted continuously and consecutively, eachoutbound message being addressed through its first and second words to aparticular mobile station, or all mobile stations. The command wordindicates the function desired of the addressed mobile station. Thisfunction may be a request for status or condition, or may be aninvitation for the mobile station to indicate that it desires totransmit to either the base station or another mobile station. As eachmobile station receives the outbound messages, it synchronizes on theoutbound messages, but only responds if its address is recognized in thefirst and second address words of a particular message. If its addressis recognized, the mobile station responds by sending a somewhat similarinbound message in binary bit form. Each inbound message comprises apreamble, the same first synchronizing word, the same first address wordtransmitted three times, the same second inverted synchronizing word,the same second address word transmitted three times, the same thirdinverted synchronizing word, and a response word transmitted threetimes. This response word indicates that the mobile station is answeringthe inquiry, either as to its status or condition, or that it wishes totransmit on a frequency. If the mobile station does desire to transmit,the base station will then send another outbound message to that mobilestation to set up or establish the desired communication. The inboundresponse from the mobile station to the base station has a bit rate thatis 11/2 times the bit rate of the outbound message rate, so that othermobile stations can respond to their outbound messages as received. Thebase station anticipates each inbound message and uses the inboundmessage preamble and the first synchronizing word to synchronize thebase station with the inbound message. Thus, high speed binary functioncontrols are reliably provided between a base station and a mobilestation in the environment of radio frequencies, particularly those ofthe land mobile service.

BRIEF DESCRIPTION OF THE DRAWING

The subject matter which we regard as our invention is particularlypointed out and distinctly claimed in the claims. The structure andoperation of our invention, together with further objects andadvantages, may be better understood from the following descriptiongiven in connection with the accompanying drawing, in which:

FIG. 1 shows a diagram illustrating an example of a radio communicationsystem utilizing function control apparatus in accordance with ourinvention;

FIG. 2 shows a schematic block diagram of a base station functioncontrol apparatus in accordance with our invention;

FIG. 3 shows a schematic block diagram of a mobile station functioncontrol apparatus in accordance with our invention;

FIG. 4 shows the outbound message format used in the function controlapparatus in accordance with our invention;

FIG. 5 shows the inbound message format used in the function controlapparatus in accordance with our invention;

FIGS. 6a through 6d show wave forms illustrating certain pulses andtheir manipulation in the operation of function control apparatus inaccordance with our invention;

FIG. 7 shows a more detailed schematic block diagram of the transmitmodem of our function control apparatus of FIG. 2;

FIG. 8 shows a more detailed schematic block diagram of the receivemodem of our function control apparatus of FIG. 2;

FIG. 8a shows a modification of a portion of the receive modem of ourfunction control apparatus of FIG. 8;

FIG. 9 shows a more detailed schematic block diagram of the transmit andreceive modem of our function control apparatus of FIG. 3;

FIG. 10 shows a more detailed schematic block diagram of a diphase tobinary converter in accordance with our invention that can be used inthe modems of FIGS. 8 and 9;

FIGS. 11a through 11f show wave forms for illustrating the operation ofthe converter of FIG. 10;

FIG. 12 shows a more detailed schematic block diagram of the encoder ofour function control apparatus of FIGS. 2 and 3; and

FIG. 13 shows a more detailed schematic block diagram of the decoder ofour function control apparatus of FIGS. 2 and 3.

DESCRIPTION OF PREFERRED EMBODIMENTS Introduction

In the following description, we will first give a general descriptionof a radio communication system having function control apparatusutilizing our invention. Then, we will give a more detailed descriptionof the function control apparatus and our inventions in that apparatus.

GENERAL DESCRIPTION

FIG. 1 shows an example of a radio communication system having functioncontrol apparatus utilizing our invention. In the example of FIG. 1, itis desirable that relatively efficient use be made of the radio spectrumwhen communicating between a fixed command or base station and one ormore controlled or mobile stations, or when communicating between mobilestations. The base station may be connected by telephone lines to otheruser locations in order to permit those other locations to connect withthe radio transmitter and receiver at the base station for communicationwith the mobile stations. While only one base station, two mobilestations, and three user telephones are shown, our apparatus can be usedwith more or less such stations or users. Because the mobile stationtransmitters are, usually, of lower power than the base stationtransmitter, satellite radio receivers may be strategically located soas to pick up transmitted signals from the mobile station transmittersand supply those signals over telephone lines to the base station. Inorder that communication can be established and completed moreefficiently between a base station and one or more mobile stations orbetween mobile stations, we have provided function control apparatus foruse with the radio communication system. Our function control apparatusutilizes relatively high speed binary or digital signals to establishthe desired communication, or to obtain information, or to indicate astatus condition. Where there are a relatively large number of radiofrequency channels available for communication, we prefer that a singlechannel be dedicated for the transmission of this binary or digitalinformation. However, it is to be understood that the binary or digitalinformation can be transmitted and received on the same radiofrequencies used for the voice communication. The base station is shownwith a data transmitter and several voice transmitters. The receiversmust be able to receive on the dedicated channel, if used, and the voicechannels. The binary or digital information transmitted is used toprovide a control function, such as the establishment of desiredcommunication between the base station and a mobile station, or betweentwo mobile stations, or to obtain information.

An example of the establishment of communication between the basestation and a mobile station is where a person at a fixed locationconnected to the base station by a telephone line desires to communicatewith a mobile station. That person can dial an appropriate number to thebase station. The base station computer than processes (includingrecording if desired) the information represented by the dialed number,provides switching, and transmits appropriate binary or digitalinformation over either the dedicated channel or the voice channel tothe desired mobile station. If the mobile station receives thetransmission and is available, the mobile station transmits a responseusing binary or digital information. The base station then directs themobile station to begin communication with the person at the fixedlocation either on the frequency used to establish the communication, oron some frequency directed by the base station. In a similar manner, thebase station can receive a response from a mobile station and establishcommunication between that mobile station and some other station, eithermobile or a user through the base station.

An example of indicating status or other condition is where a person atthe base station wishes to know whether a mobile station is inoperation, or is in some other condition. Such applications are commonin police forces where a central dispatcher wishes to know the status orcondition of one or more of his mobile police stations. In such a case,the dispatcher can send out an appropriate inquiry identifying theparticular mobile station, and the mobile station can, totally unknownto the mobile police officer, send out a reply indicating that themobile station is in service and awaiting messages, or that the mobilestation is in some other condition, such as off duty or unavailable.

The two relatively specific examples given above will suggest many otheruses and applications. Generally, the function control apparatus of ourinvention can be used in many different types of radio communicationsystems and for many different purposes in such systems, such purposesincluding without limitation the establishment of communication betweentwo stations on a radio frequency, or the inquiry as to the situation orcondition in a distant station.

FIG. 2 shows a block diagram of function control apparatus in accordancewith our invention for use in a base station of a radio communicationsystem. Functions and voice signals from either the base station or atelephone line are applied to a computer and audio switcher 10. If thebase station utilizes a separate frequency for the function signals anda separate frequency for the voice signals, the computer 10 switches thefunction signals to an interface and encoder circuit 11. The interfaceportion makes whatever conversion may be needed to provide the properelectrical relations between the computer 10 and the encoder 11. Theencoder 11 converts the function instructions received from the computer10 to the desired format in accordance with our invention, and thensupplies this format to a modem 12 for transmission by the base stationdata transmitter. After communication is established, if voicecommunication is provided, then the audio switcher 10 connects the voiceinput to the voice transmitter. Signals from the data receiver areapplied to a modem 13 which converts the received signals to binarysignals for application to an interface and decoder circuit 14. Thedecoder circuit 14 with the interface circuit converts the binaryinformation into the proper language for the computer 10. The indicatedfunctions are supplied, and after communication is established, if voicecommunication is provided, the voice receiver is connected to theappropriate lines for a voice output signal. A frequency stable clock oroscillator circuit 15 provides timing signals for the various componentsat the base station.

FIG. 3 shows a block diagram of function control apparatus in accordancewith our invention for use in a mobile station of a radio communicationsystem. The diagram of FIG. 3 is similar to that of FIG. 2. However,because a mobile station typically has only one transmitter and onereceiver, the data information must be transmitted and received by thesame transmitter and receiver used for voice communication. Typically, amobile station does not transmit when it is receiving, and does notreceive when it is transmitting, so that a single modem 16 can be used.Received data signals are applied to the modem 16, and then decoded by adecoder 14 which may be similar to the decoder 14 for the base station.Signals from the decoder 14 are applied to a control 10 which generallyprovides the same functions as the computer and audio switcher 10 inFIG. 2. The data signals so received are utilized at the mobile stationin any way desired, such as establishing a communication channel, orrequesting information from the mobile station. If the data signals areused to establish voice communication, a switch 17 connects voicesignals from the receiver to an appropriate output such as aloudspeaker. In the other direction, data signals are applied to thecontrol 10 and encoded by an encoder 11 which may be similar to theencoder 11 of FIG. 2. These encoded signals are applied to the modem 16and transmitted as data signals. If information has been requested fromthe mobile station, these data signals indicate the status or desiredinformation. If the function control is used to establish communication,the control 10 operates the switch 18 to connect voice signals to themobile station transmitter. And as in the base of the base station, afrequency stable clock or oscillator circuit 15 provides the necessarytiming signals for the mobile station.

In order that our function control apparatus can be used in variousapplications such as establishing communication channels or requestinginformation, and in order that our function control apparatus can beused in the relatively noisy and sometimes unreliable radio frequencyenvironment, we developed a function message control format to meetthose requirements and still give reliable transmission of data at arelatively rapid rate. FIG. 4 shows the format of the function controlmessages used for transmission from a base station to a mobile station.The base station may and preferably does transmit messages continuouslyand sequentially, so that message 2 is shown immediately followingmessage 1. Subsequent outbound messages would follow immediately, eachoutbound message having the same format but having unique or particularaddress and command words depending on the station to which the messageis addressed and the function or inquiry desired. If the functioncontrol apparatus is to provide communication between the stations in aradio communication system, the base station may send a messageaddressed to each mobile station in a sequence, the message inquiringwhether the mobile station desires to communicate. The sequence can, ofcourse, be repeated continuously. Or, the base station can send anaddress to all mobile stations. When its addressed message is received,a mobile station can respond to the inquiry by sending a message (to bedescribed) indicating that the mobile station does or does not desire tocommunicate. If the function control apparatus is to obtain information,the base station may send a message addressed to a mobile station, themessage inquiring as to information about or status of the mobilestation. When its addressed message is received, the mobile station canrespond to the inquiry by sending a message (to be described) thatanswers the inquiry. The messages comprise binary or digital bits in atrain or sequence. Message 1 is representative of the format of alloutbound messages, and comprises, from left to right in time sequence, asynchronizing word (abbreviated SYN), a first address word (abbreviatedADD.1) which is produced a total of three times, a logic invertedsynchronizing word (abbreviated SYN), a second address word (abbreviatedADD.1') which is produced a total of three times, a second invertedsynchronizing word (abbreviated SYN), and a command word (abbreviatedCOM.1) which is produced a total of three times. The binary or digitalmakeup of each address and command word comprises 8 message and 4 paritybits as indicated by the arrows leading from the words. It will be seenthat each message has a total of 135 binary bits. The SYN word comprisesnine binary bits 011100100, which will be recognized as a seven bitBarker code having a prefix O and a suffix O. The SYN word is, ofcourse, the logic inversion of this. The Barker code also includes thereverse sequence which, with the added prefix O and suffix O, is001001110. This sequence may serve as the SYN word, and the SYN word isthe logic inversion of this. Hence, as used in this application, theBarker code with prefix and suffix zeros may be 011100100 or 001001110.And of course, persons skilled in the art will appreciate that logicones and zeros may be interchanged, since they refer to two binarylevels, and not to a rigid voltage polarity or magnitude. Each of theaddress and command words comprises eight message bits and four paritybits whose generator polynomial is X⁴ + X + 1. The generator matrix is:

    ______________________________________                                                                        1 0 0 0 0 0 0 0 1 1 1 0                                                       0 1 0 0 0 0 0 0 0 1 1 1                                                  G   = 0 0 1 0 0 0 0 0 1 0 1 0                                                       0 0 0 1 0 0 0 0 0 1 0 1                                                      0 0 0 0 1 0 0 0 1 0 1 1                                                       0 0 0 0 0 1 0 0 1 1 0 0                                                       0 0 0 0 0 0 1 0 0 1 1 0                                                       0 0 0 0 0 0 0 1 0 0 1 1                       ______________________________________                                    

The parity check matrix is:

    ______________________________________                                                                        1 0 1 0 1 1 0 0 1 0 0 0                                                  H   =  1 1 0 1 0 1 1 0 0 1 0 0                                                     1 1 1 0 1 0 1 1 0 0 1 0                                                       0 1 0 1 1 0 0 1 0 0 0 1                       ______________________________________                                    

We have selected a bit rate of approximately 1111 bits per second, sothat each message requires approximately 121.5 milliseconds. While othermessage formats and other bit rates are possible, we prefer thosedescribed above and shown in FIG. 4.

Since a typical application of our function control apparatus transmitsoutbound messages continuously, it is relatively easy for the functioncontrol in a mobile receiver to synchronize with the transmittedoutbound message even though the message is not addressed to thatreceiver. On inbound messages, however, a mobile station generally doesnot transmit continuously, so that the base station has less opportunityto synchronize with an inbound message. Accordingly, as shown in FIG. 5,we provide our inbound message format with a binary preamble ahead ofthe 135 binary bits that provide synchronization, addresses, andresponses. In a preferred embodiment, this preamble comprises 24 bits ofalternate ones and zeros. However, other preambles may be used. In theinbound message, the 135 bits are substantially the same as the 135 bitsin the outbound message format. Thus, we prefer that the ADD.1 andADD.1' words (three times each) be identical to the outbound ADD.1 andADD.1' words, and that the response word RESP.1 (produced three times)be partly similar to the command word, and partly different to indicatethe response to that command or question. However, this is a matter ofchoice and preference, depending upon the application and environment.Since the mobile station transmits a longer message and requires sometime to respond to an address and command, we provide a time intervalbetween mobile inbound messages. Accordingly, the total of binary 159bits in our inbound message format are transmitted approximately 11/2times faster than the outbound bits, or 1666 bits per second. Hence aninbound message requires 95.2 milliseconds, which leaves a time of 26.3milliseconds between inbound messages. This time period of 26.3milliseconds is adequate and desirable in order to compensate for anydelays or responses of the mobile stations.

If a base station sends a message 1 to a given mobile station, itsoutbound message format will comprise the synchronizing word 01110100,followed by an address word for the mobile station transmitted a totalof three times. Then the inverted synchronizing code word 100011011 issent, followed by a second address word for the mobile stationtransmitted a total of three times. Then, the inverted synchronizingword 100011011 is sent followed by the command word transmitted a totalof three times. The given mobile station responds to its address wordsand command word by sending its inbound message having a preamble(preferably having 24 bits of alternate zeros and ones) to enable thebase station to bit synchronize with the inbound message. This isnecessary because an inbound message will not be repeated until asubsequent outbound message addressed for the given mobile is received.After the preamble, the inbound message has the synchronizing word011100100 followed by an address word transmitted a total of threetimes, the inverted synchronizing word, the second address wordtransmitted a total of three times, the inverted synchronizing word, andfinally the response transmitted a total of three times. And asmentioned earlier, this inbound message bit rate is 11/2 times fasterthan the outbound message bit rate, namely 1666 bits per second. Thus,the inbound message only requires 95.2 milliseconds, leaving a 26.3milliseconds space for the next message from a mobile station. Ofcourse, while the given mobile station is transmitting its message 1,the base station may be transmitting its message 2 to another mobilestation. However, the given mobile station generally will have itsreceiver disconnected from the antenna when its transmitter isoperating. Hence, message 2 should not be addressed to the same givenmobile station, but should be for a different mobile station.

The triple transmission of each address word ADD.1, each address wordADD.1', and each command word COM.1 or response word RESP.1 was providedbecause of the nature of radio communication. Such communication issubject to impulse noise and fading because of bridges, buildings, andother objects. Hence, the triple transmission provides added assurancethat the message will be received. When a message is received, and thereceiving station is in synchronization with the message, correspondingbits of each repeated word are stored, and the majority of similar bits(that is 2 or more of the 3 corresponding bits) is selected by a digitalor logic voting process. Thus, if the first bit of the first and secondwords of ADD.1 are a logic 1 but the first bit of the third word ofADD.1 is a logic 0, then our system selects the majority and decidesthat the first bit of ADD.1 is properly a logic 1. The remainder of thebits of each word are correspondingly selected, and after suchselection, the selected bits are combined and utilized as the properlogic sequence of bits. As for synchronization, we assume that if, in agiven message, the synchronizing word SYN and the logic invertedsynchronizing word SYN are received in sequence, then the receivingmobile station is in message synchronization with the transmitting basestation. The mobile station is considered to remain in synchronizationuntil five sequential synchronizing words are incorrectly received. Thisis possible because the mobile station is constantly receiving messagesfrom the base station. At the base station, however, a mobile onlytransmits its inbound message one time in response to an outboundmessage, so that the base station must synchronize on that one inboundmessage if at all possible. Hence, we have provided the inbound messagepreamble which aids bit synchronization, and alerts the base station toan inbound message. The base station then attempts to messagesynchronize on the remainder of the inbound message, and considers amessage properly received if it receives the first synchronizing wordSYN properly.

From this general description of our function control apparatus, it willbe seen that we prefer that only a base or central station transmitaddressed messages inquiring from or directing mobile stations in acommunication system. Each mobile station in the system responds only tomessages addressed to that mobile station (or to an all-stationmessage), such response being any desired function such as switching toa communication frequency or indicating a status or condition. However,we contemplate that other stations (base or mobile) in a communicationssystem may have the ability to send the inquiring or directing messagesif desired.

DETAILED DESCRIPTION -- COMPUTER AND AUDIO SWITCHING; CONTROL

We have not shown a more detailed diagram of the computer and audioswitcher 10 of FIG. 2 or the control 10 of FIG. 3 since such devices areknown and may take many different forms, depending upon the features andarrangements desired in the function control apparatus. It is for thisreason that the computer and control have been given the same referencenumeral 10. In the base station, the designated block 10 has been calleda computer because it may have to hold more information and perform morefunctions than it would in a mobile station. Both the computer andcontrol 10 store addresses and commands or responses which have apredetermined code, and which are looked up and produced in response toa relatively simple signal. For example, if a user requests his basestation to connect him with a designated mobile station, he may send asimple signal that means call mobile station 1. The computer 10 wouldlook up the address of mobile station 1 and prepare the designated codefor mobile station 1 and send it through the interface and encoder 11and the modem 12 to the data transmitter. All mobile stations mayreceive the transmitted message, and those that do receive the messagecompare its address with the stored mobile address. We prefer that eachmobile station have a unique address, so that only one mobile stationacts on a particular message. However, a unique address for all mobilestations may be provided to call all mobile stations simultaneously.Mobile station 1 compares the transmitted address with its address, andfinding them the same, transmits a reply. On receiving this reply, thebase station computer 10 would compare the mobile station reply with theinformation transmitted and if the signals transmitted and received areproper, the computer 10 would operate its audio switcher and connect theuser to mobile station 1. The computer 10 may also make a record of thecall or operation. A similar operation may be provided by the control 10in the mobile station. We have shown separate switches 17, 18 for themobile station, but they perform essentially the same function as theaudio switcher in the computer 10. The audio switcher in the computer 10may be a more complicated device, since it may switch a number ofincoming lines to a number of outgoing base station transmitters andreceivers such as shown in FIG. 1.

The computer or control 10 is the element where functions and commandsare initiated and manifested. This includes an inquiry from the basestation to the mobile station; comparisons of addresses and commands;establishment of a communication channel, on either the data designatedchannel or on another channel, between the base station and a mobilestation or between mobile stations; and any other functions which mightbe desired in a customer-subscriber arrangement. Hence the number offunctions desired determine the capabilities which the computer orcontrol 10 must provide. It is for this reason that we have simplydesignated the input and outputs to the computer or control as afunction in or a function out. Such functions can be of almost any type,depending upon the application or purpose of the radio communicationsystem. Such techniques are well known to persons skilled in the art,and need not be described.

DETAILED DESCRIPTION -- MODEM

At this point, it is appropriate to describe the binary bits or pulseswhich we prefer to be used in our function control apparatus. The pulsesare shown in the waveforms of FIG. 6 which are plotted along a commontime axis. In FIG. 6 (a), we have shown what we consider binary pulses,that is pulses which alternate between two values designated a logic 0and a logic 1. It is immaterial whether the upper value is considered alogic 1 and the lower values a logic 0, or whether the upper value isconsidered a logic 0 and the lower value is considered a logic 1. Wehave assumed that the upper value is a binary logic 1, and the lowervalue is a binary logic 0. The pulses shown in FIG. 6 (a) represent atypical train of binary pulses which would be produced by the computeror control 10 and the encoder 11. Such pulses are not desirable whenthey have to be transmitted over a radio or other paths which cannoteasily transmit direct current. Accordingly, the binary pulses of FIG. 6(a) are converted to what we call diphase pulses as shown in FIG. 6 (b).Corresponding binary and diphase pulses are respectively above and beloweach other. The diphase pulses carry the same information, but have avoltage transition at the end of each binary pulse, and a voltagetransition in the middle of either a binary logic 0 or a binary logic 1.In FIG. 6 (b), we have assumed that the middle transition is providedfor a binary logic 1. Hence, it will be seen that the diphase pulseshave a transition, either up or down, at the end of each binary pulse,and also have a transition, either up or down, at approximately themiddle of each logic 1 binary pulse. These added transitions providemore alternating current components, and are readily adaptable to beingtransmitted by radio paths or communication paths which are intended tocarry alternating current signals. Conversion from binary to diphasepulses and from diphase to binary pulses is a known technique. FIGS.6(c) and 6(d) will be discussed subsequently.

With respect to FIG. 2, we have assumed that the base station isconstantly transmitting outbound messages and is or may be constantlyreceiving inbound messages. Accordingly, the base station of FIG. 2 hasa transmitting modem 12 and a receiving modem 13. On the other hand, wehave assumed that the mobile station is either transmitting orreceiving, so that the common modem 16 may be provided for the mobilestation as shown in FIG. 3. The following description covers thetransmitting and receiving modems. It should be pointed out that at agiven station, the modems may be combined or may be separate, dependingupon the circumstances and needs at that station.

FIG. 7 shows a block diagram of the transmit modem 12 used in the basestation. This modem receives binary pulses, such as shown in FIG. 6(a),from the encoder 11, and these pulses are applied to a binary to diphaseconverter 30. The converter 30 transforms the binary pulses to diphasepulses as shown in FIG. 6(b). This transformation is made by any of theknown converter circuits, utilizing clock pulses at the 1111 bits persecond or C1111 rate. As used in this application, clock pulses areindicated by the prefix C followed by a number which indicates thefrequency. Thus, C400,000 indicates clock pulses at the rate of 400,000pulses per second. The C400,000 clock pulses are provided by the clock15 in the base station, and these pulses are divided by a 360 divider 31to produce the C1111 pulses.

FIG. 8 shows a block diagram of the receive modem 13 for the basestation. FIG. 8 includes more blocks or components, because this modem13 provides synchronizing signals and adjusted clock signals. Itsprimary function however, is to convert diphase pulses, such as shown inFIG. 6(b), to binary pulses, such as shown in FIG. 6(a), for use in thebase station decoder 14. The received diphase pulses are converted tobinary pulses by a converter 35 which may be of a known type or one tobe described hereinafter. The binary pulses are applied to a nine bitshift register 36 which is used in voting on the pulses in the SYN wordto provide an indication that the base station apparatus is synchronizedwith the inbound message from the mobile station.

A primary requisite for this synchronization is that a stable frequencyhaving the same bit rate and phase as the incoming diphase pulses besupplied to the base station function control apparatus. This frequencyis achieved by means of the clock 15 which supplies the C400,000 pulses.These pulses are divided and converted to two sets of pulses preferablyhaving a 180° phase relation, by means of a divide by six divider 37which provides C66666φ1 and C66666φ2 pulses, where φ1 and φ2 mayindicate 0° and 180° phases respectively. These pulses are respectivelyapplied to a normally open gate 38 and a normally closed gate 39. Thenormally open gate 38 may be closed by a lead signal produced by a phasecomparator 40, and the normally closed gate 39 may be opened by a lagsignal produced by the phase comparator 40. The C66666φ1 and C66666φ2pulses passed by the gates 38, 39 are combined sequentially in an adder41 and then divided by a divide by 10 divider 42 to produce a sequenceof C6666 pulses. These pulses are further divided by dividers 43, 44 tosupply adjusted clock pulses C1666. These adjusted clock pulses areutilized in the decoder and other parts of the base station receiveapparatus and are also applied to one input of the phase comparator 40.The received diphase pulses at the nominal 1666 bits per second rate areapplied to a data rate converter 45 which may take a number of knownforms. The converter 45 senses the data rate of the diphase pulses ofFIG. 6(b), and omits the intermediate logic 1 transitions. The output ofthe converter 45 for the applied diphase pulses is shown in FIG. 6(c).This output is applied to the other input of the phase comparator 40which compares the phase of the adjusted clock pulses C1666 with thephase of the received data rate pulses. If the phase of the adjustedclock pulses C1666 lags the phase of the data rate pulses, as shown inthe left portion of FIG. 6(d), then the phase comparator 40 produces alag signal that opens the gate 39 to add some C66666φ2 pulses to thepulse train. These added pulses, when divided, result in the adjustedclock signal coinciding in phase with the data rate pulses as indicatedat the time T1 in FIGS. 6(b), 6(c), and 6(d). Conversely, if the phaseof the adjusted clock pulses leads the phase of the data rate pulses, asshown at the right portion of FIG. 6(d), the phase comparator 40produces a lead signal which closes the normally open gate 38 to blocksome C66666φ1 pulses. This reduces the number of pulses in the train.After these pulses are divided, the phase of the adjusted clock pulsescoincides with the phase of the data rate pulses as indicated at thetime T2 in FIGS. 6(b), 6(c), and 6(d). Thus, the reliable and stablepulses supplied by the clock 15 have their leading edge or phaseadjusted so that they coincide with the incoming diphase pulses from thereceiver. These adjusted clock pulses are utilized in various parts ofthe apparatus, particularly the decoder 14 and an apparatus signalgenerator 47.

As mentioned previously, the base station function control apparatusmust synchronize with an inbound message very quickly, as typically theinbound message may not be repeated until a considerable number ofintervening inbound messages have been sent to the base station by othermobile stations. It is for this reason that we have provided the 24 bitpreamble to each inbound message as shown in FIG. 5 to assist the basestation in achieving bit synchronization. Generally, the base stationwill have some internal timing circuit or device that alerts the basestation to the time it should be receiving a preamble from a givenmobile station in response to the predetermined outbound message to thegiven mobile station. At the proper time, the base station beginslooking for this preamble from the given mobile station. When received,the preamble and message bits of an inbound message are passed throughthe nine bit shift register 36. Each first bit output, each invertedfourth bit output, and each inverted seventh bit output of the shiftregister 36 are applied to a voter circuit 48. Thus, the voter circuit48 determines the binary value of each bit in each group of threeequally spaced bits, and produces a binary value representing themajority binary value of those bits. For example, if two or more of thethree bits in a group are a logic 1, the voter circuit 48 applies alogic 1 to a three bit shift register 49. If two or more of the threebits in a group are a logic zero, the voter circuit 48 applies a logiczero to the three bit shift register 49. The following table andexplanation will explain how the base station operates on the firstsynchronizing word SYN to put the base station function controlapparatus in synchronization with the inbound message:

                  TABLE 1                                                         ______________________________________                                        Synchronizing Code Bits:                                                      1      2     3     4    5   6   7    8   9   Majority Vote                    ______________________________________                                        (1)  0     1     1   1    0   0   1    0   0                                                       INV.         INV.                                        (2)  0               0            0            0                              (3)  1     1     1   0    0   1   0    0   X                                                       INV.         INV.                                        (4)  1               1            1            1                              (5)  1     1     0   0    1   0   0    X   Y                                                       INV.         INV.                                        (6)  1               1            1            1                              ______________________________________                                    

As the sequence of bits from the converter 35 passes through the shiftregister 36 at the C1666 pulse rate, the first, fourth, and seventh bitsof the shift register output are considered and voted on. In line 1 ofTable 1, we have assumed that our nine bit synchronizing code 011100100is completely entered in the shift register 36. In this condition, thefirst bit of the synchronizing code is at the first shift registeroutput, the fourth bit of the synchronizing code is at the fourth shiftregister output, and the seventh bit of the synchronizing code is at theseventh shift register output. After the fourth and seventh bits areinverted, line 2 shows the logic on which the voter 48 votes. Asindicated, all three bits are at a logic 0 so that the voter produces alogic 0. In line 3, another bit X has been received by the register sothat the first bit (a 0) of the code is shifted out. At this time, thesecond, fifth, and eighth bits of the code word are at the first,fourth, and seventh shift register outputs, so that these outputs are atlogic 1, 0 and 0 respectively. After inversion, the voter 48 sees thebits shown in line 4, all of which are a logic 1 so that the voter 48produces a logic 1. In line 5, another bit Y is received and the secondbit (a 1) of the code is shifted out. At this time, the third, sixth,and ninth bits of the code word are at the shift register output, sothat after inversion, as shown in line 6, the voter 48 sees three logic1's so that the voter 48 produces a logic 1. The right hand column ofTable 1 shows that the majority vote is 011, based on the best two outof three bits for each vote. In summary, we provide an IN SYNC signal ifa majority voted sequence of 011 is received after the preamble. Thissequence is highly unique, so that the chances of an error are reducedconsiderably by our nine bit synchronizing word 011100100. Voting of thefirst, fourth, and seventh bit outputs is a continuous operation, butthe uniqueness of the synchronizing word and the majority voting insuresynchronizing on almost all inbound messages. The voted bits are appliedto a three bit shift register 49. When the three bit shift register 49shows an 011 at its outputs, an 011 detector 50 produces an appropriatein-synchronization signal, designated IN SYNC in FIG. 8. Thissynchronizing signal indicates that a command word will begin with thenext bit received after the synchronizing code. The signal is applied tothe apparatus signal generator 47 along with the adjusted clock so as toprovide appropriate signals for use in the base station function controlapparatus. It will be appreciated that in the voting process justdescribed, the first register output may be inverted and the fourth andseventh register outputs left normal, as shown in FIG. 8a. In this case,an IN SYNC signal would be produced if a majority voted sequence of 100is received. If the synchronizing word is 001001110, the majority votedsequence would be 001 for an inverted seventh register output or wouldbe 110 for inverted first and fourth register outputs. In the abovedescription, we refer to one or more of the first, fourth, and seventhshift register 36 outputs being inverted. The net result of this is thatthe first, second, and third code bits appear inverted if the firstshift register output is inverted, and the fourth through ninth codebits appear inverted if the fourth and seventh shift register outputsare inverted. And in this and other discussions, the use of logic 1 andlogic 0 simply means any two binary levels, such as plus and zerovoltages, zero and minus voltages, or plus and minus voltages.

From the message in-synchronization signal, and with reference to theformat of FIG. 5, the generator 47 produces a function word signal atthe beginning of each of the address words and the response word, a bitvoter signal to indicate to the decoder 14 that three corresponding bitsof a repeated word are present and should be voted on, a parity signalto indicate that the four parity bits in a 12 bit word have beenreceived and corrections should be made, and a first word signal toindicate the first of the three repeated address or response words.

In the description of the receive modem 13 of FIG. 8, we have usedterminology and designations which, we feel, aid in understanding themodem 13. Persons skilled in the art will appreciate that other logic oroperating functions can be substituted. For example, the shift register36 actually only needs to be able to store six bits, as the seventh bitcan be voted on as it is received from the converter 35. Similarly,other divide circuits could be used in order to achieve the desired bitrate. And, of course, other bit rates may be utilized.

In the mobile station, the modem is generally similar except for thefact that a mobile station is usually receiving outbound messagesconstantly one after another, whether they are designated for that givenmobile station or not. These outbound messages provide moreopportunities for the mobile station to synchronize its function controlapparatus with the base station pulses or bits and messages. Anotherdifference is the fact that the mobile station receives pulses at theoutbound message rate of 1111 bits per second, and transmits pulses backat the inbound message rate of 1666 bits per second, which is 11/2 timesas fast. Finally, the modem for the mobile station may combine thetransmitting and receiving portions, since generally the mobile stationis either transmitting or receiving, but not both transmitting andreceiving as in the case of a base station.

FIG. 9 shows a block diagram of the modem 16 for a mobile station. Partscorresponding to those of FIG. 8 have been given the same referencenumerals. In the lower part of FIG. 9, the clock signals are divided andpulses added or deleted by the gates 38, 39 depending upon the phaserelation of the clock and diphase pulses applied to the phase comparator40. The diphase pulses are also applied to the converter 35 and the ninebit shift register 36. The binary pulses so produced are applied to themobile station decoder 14. The mobile station can synchronize itsfunction control apparatus with outbound messages more reliably, as itmay be constantly receiving outbound messages even though not addressedto it. A synchronizing and inverted synchronizing word sensor 55 looksat each nine bits in the register 36. If the proper synchronizing word011100100 is received followed by the proper inverted synchronizing word100011011, the sensor 55 produces an insynchronization (IN SYNC) signalfor use in the function control apparatus and in the apparatus signalgenerator 47. The apparatus produces this in-synchronization signaluntil an error counter 56 receives and counts a total of fiveconsecutive errors in synchronizing words or inverted synchronizingwords. We prefer five consecutive errors, because of the nature of thecommunication medium. It is quite possible that several synchronizingerrors could be received without the function control apparatus gettingout of synchronization. If a correct synchronizing word or a correctinverted synchronizing word is received before five consecutive errorsare counted, the sensor 55 produces a recount signal which sets thecounter 56 back to zero so that the error count is started over again.However, if the counter 56 does count five consecutive synchronizingerrors, it provides a reset signal to the sensor 55, which causes thesensor 55 to produce an out-of-synchronization signal (or remove theinsynchronization signal) until a correct synchronizing word followed bya correct inverted synchronizing word are received. As mentioned before,the synchronizing code may have the bit values 001001110 and invertedbit values 110110001.

In the transmitting direction, the binary pulses from the encoder 11 atthe 11/2 times or 1666 bits per second rate are applied to the converter30 which is the same as the converter 30 of FIG. 7. This converter 30receives adjusted clock pulses C3333, since the mobile station clock isadjusted in accordance with outbound messages. These pulses are derivedfrom the divide by 10 divider 42 and applied to a divide by 4 divider 57to produce C1666 clock pulses for the converter 30.

DETAILED DESCRIPTION -- MODEM DIPHASE TO BINARY CONVERTER

While there are known diphase to binary converters which can be used forthe converters 35 in FIG. 8 and FIG. 9, we have provided a converterwhich, we believe, improves the message acceptance rate when a dataformat such as previously described is used. When binary or digitalpulses are transmitted over radio paths, resultant errors are primarilydue to multipath fading of the radio frequency signal. When, as in ourfunction control apparatus, majority voting of repeated pulses is usedto improve the accuracy of such received pulses, any arrangement whichproduces a negative or zero correlation of errors will enhance theaccuracy of the voted bits. Normally the occurrence of multipath fadesis predictable; therefore the errors follow a predictable or correlatedpattern. Our diphase to binary converter will produce either zero or twobinary errors for each diphase error. The probability that a doublebinary error will occur when a diphase error occurs is 0.5. Hence, thetotal number of bit errors due to multipath fading is the same as adiphase to binary converter with a one-to-one error correspondence, butthe number of voted errors is less since the errors are not correlated.The converter shown in FIG. 10 produces a negative or zero correlationof errors and thus improves the voted bit probability. In FIG. 10 wehave provided three D type flip-flops FF1, FF2, FF3. These flip-flopsare of the bistable type and are triggered or clocked at their clockinput C by pulses which have a rate twice the binary pulse rate. Thediphase pulses from the receiver are applied to the D input of the firstfip-flop FF1. The Q output of the first flip-flop FF1 is applied to theD input of the second flip-flop FF2, and the Q output of the secondflip-flop FF2 is applied to the D input of the third flip-flop FF3. TheQ outputs of the first and third flip-flops FF1, FF3 are applied to thetwo inputs of an exclusive OR gate EOR, and the output of this gate EORis inverted. This inverted output is applied to the shift register 36 inFIG. 8 or FIG. 9. As known in the art, an exclusive OR gate produces alogic 0 when its inputs have the same logic level, that is all inputsare at logic 0 or all inputs are at a logic 1. An exclusive OR gateproduces a logic 1 output when its inputs are at different logic levels.The combination of the exclusive OR gate EOR and the inverter results ina logic 1 being produced when both inputs to the exclusive OR gate EORare at the same logic level, and a logic 0 being produced when bothinputs to the exclusive OR gate EOR are at different logic levels.

It will be seen that the flip-flops FF1 through FF3 provide a way toshift the phase or time delay diphase pulses so that two signalsidentical to the diphase input can be produced that have a 360° (or onebinary bit) phase relation. The exclusive OR gate EOR provides a way toproduce one binary logic output when the two inputs are different, andto produce the other binary logic output when the two inputs are thesame. This can be shown by the following truth table:

    ______________________________________                                         FF1           FF3        I                                                   Q              Q          OUTPUT                                              ______________________________________                                        0              0          1                                                   1              0          0                                                   1              1          1                                                   0              1          0                                                   ______________________________________                                    

The following explanation of our converter of FIG. 10 is given with thewaveforms shown in FIG. 11. FIG. 11(a) shows the binary pulse rate, andthis can be any rate, such as 1111 bits per second or 1666 bits persecond, as mentioned earlier. The outputs of the three flip-flops FF1,FF2, FF3 are shown in FIGS. 11(b), 11(c), and 11(d), and it will be seenthat each flip-flop introduces a 180° time delay between its input andoutput pulses. Thus, the output of the flip-flop FF3 is 360° or onebinary time period delayed with respect to the output of the flip-flopFF1. FIG. 11(e) shows the applied clock pulses, which are at twice thebinary pulse rate. The inputs to the exclusive OR gate EOR are derivedfrom the outputs of the first and third flip-flops FF1, FF3. Just beforethe time T1, it will be seen that both these outputs are at a logic 1,so that the exclusive OR gate EOR produces a logic 0 which is invertedby the inverter to a logic 1. This logic 1 is a binary pulse and isshown in FIG. 11(f) prior to the time T1. Immediately after the time T1,the flip-flop FF1 is still producing a logic 1 but the flip-flop FF3 isproducing a logic 0, so that the exclusive OR gate produces a logic 1which is inverted to a logic 0 as shown in FIG. 11(f). Immediately afterthe time T2, the flip-flop FF1 is producing a logic 0 but the flip-flopFF3 is producing a logic 1 so that the inverted output remains a logic0. Immediately after the time T3, the flip-flop FF1 is producing a logic1 and the flip-flop FF3 is producing a logic 1. Hence, the binary pulseof FIG. 11(f) switches to a logic 1. Immediately after the time T4, theflip-flop FF1 and the flip-flop FF3 are both producing a logic 0. Theexclusive OR gate EOR produces a logic 0 which is inverted to a logic 1.Subsequent changes in the binary pulses are produced in a similarmanner. Thus, the diphase input, such as represented in the waveform ofFIG. 11(b), is converted to binary pulses as represented in the waveformof FIG. 11(f).

Although the converter circuit of FIG. 10 is relatively simple, we havefound that when this converter is used in a voting arrangement such aswe utilize in our function control apparatus, the accuracy oftransmitted binary or digital data is greatly increased, particularlywhere the transmission path is noisy or is subject to fading, such as inthe land mobile radio frequency spectrum.

DETAILED DESCRIPTION -- ENCODER

The encoder 11 for the base station is intended to receive words(address and command of eight bits each) from the computer 10 andgenerate an outbound message format such as shown in FIG. 4. Similarly,the encoder 11 for the mobile station receives words (address andresponse of eight bits each) from the control 10 and generates aninbound message format such as shown in FIG. 5. Such encoders may take anumber of known forms which, generally, provide the necessary pulse andtiming sequences to produce those formats. FIG. 12 shows a relativelysimple diagram of such an encoder. Words from the computer or control 10are applied to a suitable storage device 65 which retains each word forthe needed length of time. A parity generator 66 is connected to thestorage device 65 and generates, on the basis of the stored eight bitword, the necessary sequence of four parity bits to be supplied afterthe eight word bits. The storage device 65 also causes a functiongenerator 67 to repeat the necessary sequence of eight word bits. Last,a preamble-synchronizing generator 68 generates the preamble bits forinbound messages, and generates the synchronizing and invertedsynchronizing bits for both inbound and outbound messages. The outputsfrom the parity generator 66, the function generator 67, and thepreamble-synchronizing generator 68 are combined in a sequencing circuit69 in the proper sequence and under time control of either the basestation clock which is absolute or under control of the mobile stationclock which is corrected in accordance with outbound messages. Ofcourse, the time control provides the proper rate, namely 1111 pulsesper second for outbound messages, and 1666 bits per second for inboundmessages. The sequencing circuit 69 also provides the necessaryrepetition of the function words, namely address 1, address 1', andcommand or response 1. The pulse sequence so produced is applied to themodem for transmission.

DETAILED DESCRIPTION -- DECODER

A diagram of a decoder 14 which can be used with the base station ofFIG. 8 or the mobile station of FIG. 9 is shown in FIG. 13. This decoderreceives the binary pulses from the modem shift register 36 at afunction word gate 72 which permits only the function words to pass fromthe shaft register to a 36 bit shift register 73. At the base station,the gate 72 blocks the preamble bits. At both the base and mobilestations, the gate 72 blocks the synchronizing bits. Pulses passed bythe gate 72 are applied to a 36 bit shift register 73. The shiftregister 73 need not actually hold 36 bits, but is being described as a36 bit register in order to simplify the explanation. Corresponding bitsof each 12 bit word of a function address or command are voted on by avoting circuit 74. This voting is provided by deriving bits 1, 13 and 25from the shift register 73, so that as the bits are shifted into andthrough the register 73, the corresponding bits (separated by 12intermediate bits) are voted on. The voter 74 votes the majority, namely2 out of 3, of the bits present at the 1, 13 and 25 outputs of theregister 73, and supplies the majority voted bit to another 12 bit shiftregister 75. The register 75 stores the voted 12 bits, in order that alogic correction circuit 76 can consider the eight message bits inrelation to the four parity bits, and do whatever bit correction may benecessary. After this correction is made, the four parity bits may bestripped off or eliminated, and the eight message bits can be providedeither in parallel or in series to the computer or control 10. If thecorrect address is received by the computer or control 10, then thecomputer or control 10 provides the necessary function, whatever it maybe as determined by the command portion of the message. At the mobilestation, this may include transmitting back the given mobile station'saddress along with the response to the command. However, other featuresor functions may be provided if desired.

As mentioned, the shift register 73 actually need not store 36 bits, butmay only store 24 bits, in which case the first and thirteenth bits arecompared and voted on along with the incoming bit which would be thetwenty-fifth bit. This would eliminate one set of 12 bit registers.However, this is a matter that is obvious to a person of ordinary skill,so that various arrangements may be utilized.

CONCLUSION

It will thus be seen that we have provided a new and improved functioncontrol apparatus which is particularly useful and adaptable to radiocommunication systems. Our apparatus provides all of the speed andversatility of modern binary digital techniques, but is also reliableand accurate, even though it is used in the relatively noisy and harshradio communication environment. While we have shown specificembodiments, persons skilled in the digital and logic art willappreciate that modifications may be made to various combinations or allof our invention. Therefore, it is to be understood that modificationsmay be made to the embodiments shown without departing from the spiritof the invention or from the scope of the claims.

What we claim as new and desire to secure by Letters Patent of the U.S. is:
 1. For use in a radio communication system having at least a base station transmitter and receiver at one location and a mobile station transmitter and receiver at a second location, function control apparatus for establishing communication between said stations comprising:a. means for for producing outbound messages having a sequence of binary bits at a first rate, each outbound message comprising a first synchronizing word of S bits, where S is an integer greater than two, a first address word, a second synchronizing word of S bits that is the binary inversion of said first synchronizing word, a second address word, a third synchronizing word of S bits that is the binary inversion of said first synchronizing word, and a command word; b. means connected to said outbound message producing means and for connection to said base station transmitter for supplying said outbound messages thereto; c. means for connection to said mobile station receiver for deriving said outbound messages transmitted by said base station transmitter and received by said mobile station receiver; d. synchronizing means connected to said deriving means of said mobile station receiver for producing an in-synchronization signal in response to said first synchronizing word and said second synchronizing word of said received outbound messages each having a respective predetermined sequence of binary values and for producing an out-of-synchronization signal in response to a predetermined plurality of sequential synchronizing words of said received outbound messages each having a sequence of binary values that is different from its respective predetermined sequence of binary values; e. means connected to said synchronizing means of said mobile station and connected to said deriving means of said mobile station for producing an inbound message in response to said in-synchronization signal and in response to said first and second address words of an outbound message having a predetermined sequence of binary values, said inbound message having a sequence of binary bits at a second rate that is greater than said first rate of said binary bits of said outbound messages, each inbound message comprising a synchronizing preamble, said first synchronizing word of S bits, said first address word, said second synchronizing word of S bits, said second address word, said third synchronizing word of S bits, and a response word; f. means connected to said inbound message producing means and for connection to said mobile station transmitter for applying said inbound message thereto; g. means for connection to said base station receiver for deriving an inbound message transmitted by said mobile station transmitter and received by said base station receiver; h. synchronizing means connected to said deriving means of said base station for determining the binary values of each group of N equally spaced bits in said synchronizing words of said inbound message, where N is an integer greater than two, and S/N is an integer greater than one; producing a bit representing the majority binary value of said N bits of each of said groups; and producing an in-synchronization signal in response to said representative bits having a predetermined sequence of binary values; i. and utilizing means connected to said synchronizing means of said base station for utilizing said derived inbound message in response to said in-synchronization signal produced by said synchronizing means of said base station.
 2. The function control apparatus of claim 1 wherein S is nine and wherein N is three.
 3. The function control apparatus of claim 1 wherein each of said first synchronizing words of all messages comprises nine bits having the binary values 011100100, and wherein there are three groups comprising the first, fourth, and seventh bits, the second, fifth, and eighth bits, and the third, sixth, and ninth bits respectively.
 4. The function control apparatus of claim 3 wherein the binary values of each group are determined by the first through third bits and the fourth through ninth bits being logically inverted relative to each other.
 5. The function control apparatus of claim 4 wherein said second bit rate is one and one-half times said first bit rate.
 6. In a communication system having at least one command station transmitter and receiver and a plurality of controlled stations, each having a transmitter and receiver, apparatus for establishing communication between said command station and one of said controlled stations comprising:a. first means for connection to said command station transmitter for applying binary outbound messages thereto, each of said outbound messages comprising a first synchronizing word of nine bits, a first address word, a second synchronizing word of nine bits that is the logic inversion of said first synchronizing word, a second address word, a third synchronizing word of nine bits that is the logic inversion of said first synchronizing word, and a command word in that order; b. second means for connection to said one controlled station receiver for deriving said outbound messages received thereby; c. third means connected to said second means for indicating proper receipt of at least said first and second synchronizing words and producing an in-synchronization signal; d. fourth means connected to said second and third means for producing a binary inbound message in response to an in-synchronization signal and in response to said first and second address words of said outbound message being designated for said one controlled station, said binary inbound message comprising a preamble, said first synchronizing word, said first address word, said second synchronizing word, said second address word, said third synchronizing word, and a response word in that order, the binary rate of said inbound message being greater than the binary rate of said outbound message; e. fifth means for connecting said fourth means to said controlled station transmitter for applying said inbound message thereto; f. sixth means for connection to said command station receiver for deriving said inbound message received thereby; g. seventh means connected to said sixth means for voting on the logic majority of a group formed of every first, fourth and seventh bits, a group formed of every second, fifth and eighth bits, and a group formed of every third, sixth, and ninth bits forming said synchronizing words; h. eighth means connected to said seventh means for producing an in-synchronization signal in response to the logic majority of said three groups having a predetermined code; i. and ninth means connected to said sixth means and to said eighth means for utilizing said inbound message in response to said in-synchronization signal.
 7. The function control apparatus of claim 6 wherein each of said first synchronizing words of all messages comprises the binary values
 011100100. 8. The function control apparatus of claim 7 wherein said seventh means votes on the binary values of said first through third bits and said fourth through ninth bits being logically inverted relative to each other.
 9. The function control apparatus of claim 8 wherein said binary rate of said inbound message is one and one-half times said binary rate of said outbound message.
 10. For use in a radio communication system having at least a transmitter at one location that transmits a synchronizing word of nine binary bits in a sequence, and a receiver at a second location for receiving said synchronizing word, apparatus for indicating that said receiver is synchronized with said transmitter comprising:a. first means for connection to said receiver for deriving as a group every first, fourth, and seventh bit as said sequence of bits received by said receiver progresses through said first means; b. second means connected to said first means for inverting the binary value of said derived fourth bit; c. third means connected to said first means for inverting the binary value of said derived seventh bit; d. voting means connected to said first, second, and third means for determining the majority binary value of each group comprising said first derived bit, said inverted fourth derived bit, and said inverted seventh derived bit; e. storage means connected to said voting means for storing each determined majority binary value; f. and indicating means connected to said storage means for indicating that the stored binary values have a predetermined code.
 11. The indicating apparatus of claim 10 wherein said indicating means comprise means for indicating that three stored binary values have a predetermined code.
 12. The indicating apparatus of claim 10 wherein said predetermined code is
 011. 13. For use in a radio communication system having at least a transmitter at one location that transmits a synchronizing word of nine binary bits in a sequence, and a receiver at a second location for receiving said synchronizing word, apparatus for indicating that said receiver is synchronized with said transmitter comprising:a. first means for connection to said receiver for deriving as a group every first, fourth, and seventh bit as said sequence of bits received by said receiver progresses through said first means; b. second means connected to said first means for inverting the binary value of said derived first bit; c. voting means connected to said first and second means for determining the majority binary value of each group comprising said inverted first derived bit, said fourth derived bit, and said seventh derived bit; d. storage means connected to said voting means for storing each determined majority binary value; e. and indicating means connected to said storage means for indicating that the stored binary values have a predetermined code.
 14. The indicating apparatus of claim 13 wherein said indicating means comprise means for indicating that three stored binary values have a predetermined code.
 15. The indicating apparatus of claim 13 wherein said predetermined code is
 100. 16. For use in a radio communication system having at least a transmitter at one location that transmits a synchronizing word of nine bit values in a sequence, and a receiver at a second location for receiving said synchronizing word, apparatus for indicating that said receiver and said transmitter are in synchronization comprising:a. first means for connection to said receiver for deriving at least one received synchronizing word therefrom; b. second means connected to said first means for inverting the binary bit values of the fourth, fifth, sixth, seventh, eighth, and ninth bits of said synchronizing word as said sequence progresses through said first means; c. third means connected to said first means and to said second means for producing a first signal representing the logic majority of a normal first, inverted fourth, and inverted seventh bits of said sequence; a second signal representing the logic majority of a normal second, inverted fifth, and inverted eighth bits of said sequence; a third signal representing the logic majority of a normal third, inverted sixth, and inverted ninth bits of said sequence; d. and fourth means connected to said third means for producing an in-synchronization signal in response to said first, second, and third signals having predetermined values.
 17. For use in a radio communication system having at least a transmitter at one location that transmits a synchronizing word of nine bit values in a sequence, and a receiver at a second location for receiving said synchronizing word, apparatus for indicating that said receiver and said transmitter are in synchronization comprising:a. first means for connection to said receiver for deriving at least one received synchronizing word therefrom; b. second means connected to said first means for inverting the binary bit values of the first, second, and third bits of said synchronizing word as said sequence progresses through said first means; c. third means connected to said first means and to said second means for producing a first signal representing the logic majority of an inverted first, normal fourth, and normal seventh bits of said sequence; a second signal representing the logic majority of an inverted second, normal fifth, and normal eighth bits of said sequence; a third signal representing the logic majority of an inverted third, normal sixth, and normal ninth bits of said sequence; d. and fourth means connected to said third means for producing an in-synchronization signal in response to said first, second, and third signals having predetermined values. 